Although the AIDS epidemic has not devastated Latin America to the degree seen in other parts of the world, there is concern that unless consistent prevention efforts are made now it can wreak havoc on the continent in the coming decade. In Argentina, it is estimated that there are 130,000 HIV-infected adults resulting in a prevalence rate of 0.7%, which matches Brazil's for highest in South America. Among high-risk men, HIV prevalence can reach as high as 13.8%. Yet, there is a dearth of knowledge concerning psychosocial and contextual factors associated with unsafe sex on which to base HIV-prevention programs. This gap in knowledge will be addressed by our study. Targeting high-risk men living in Buenos Aires, the Primary Aims of our study are to (1) assess cognitive, emotional, socio-cultural, and contextual predictors of HIV-related risk behavior;(2) assess patterns of HIV testing in the high-risk male population and factors that facilitate or hinder testing;and (3) assess prevalence and incidence of HIV and STI infections. Overall, the study seeks to foster a mutually enriching collaborative relationship between the US- and Argentina-based research partners on which to build a future intervention program to decrease risk behavior among men in Argentina. This will be a 4.5- year study consisting of two phases: a formative phase and an assessment phase. The formative phase, which will be qualitative in nature, will consist of: (a) individual in-depth interviews with System Representatives and Gatekeepers;(b) focus groups and individual interviews with high risk men;and (c) site observations of places where men meet. During the assessment phase, 500 systematically recruited men from the Buenos Aires metropolitan area will undergo (a) a theoretically-based assessment of risk behavior and its psychosocial and contextual predictors as well as barriers and facilitators of HIV testing, and (b) HIV and STI testing. During this assessment phase, we will use both Respondent Driven Sampling to recruit an unbiased sample and CASI technology to minimize respondent bias. Grounded theory will guide the qualitative data analysis, and quantitative data analysis will include GLM, GEE, and linear and logistic regression methods. By the end of the study, we will have solid data that will serve as the basis for the development of HIV prevention programs specifically designed for high-risk men in Buenos Aires. This study will contribute to identifying psychological, cultural, and environmental factors that encourage HIV-risk behavior among men in Argentina. This is a fundamental step prior to designing programs that mitigate those factors and result in decreased risk.